Numerous processes have been proposed for making fuels for jet engines from a wide range of raw materials.
In general, fuel for jet engines or jet engine fuel is produced from a kerosene fraction obtained by straight atmospheric distillation of crude petroleum and distilling between 140 and 300.degree. C. and more typically between 150 and 270.degree. C. This fraction is then treated in a desulfurization unit or in a unit for converting mercaptans into disulfides.
Another manufacturing process consists of hydrocracking a fraction of vacuum distillate. Fractionation of the effluents then affords a jet engine fuel requiring no further treatments. The jet engine fuel thus obtained, however, has very low lubricating power, i.e., insufficient for said fuel to be used in jet engines in its pure state. For this reason, said fuel must be blended with other jet engine fuels, particularly those obtained by straight distillation, which have better lubricating power and thus compensate for this deficiency.
Jet engine fuels are meant to feed the burners of aircraft turbojet and jet engines. To this end, the jet engine fuels must have certain properties. In particular, jet engine fuel Jet A1, which is the jet engine fuel most commonly used in commercial aviation, definitely must have a sulfur content of less than 0.30 wt %, a content of aromatic compounds of less than 22% by volume, a flash point above 38.degree. C., a smoke point above 25 mm and a decongealing point below -47.degree. C. According to the prior art manufacturing processes, jet engine fuels have similar energy qualities and a lower heating value per unit volume, namely less than 34.60 Mj/liter. Other properties of jet engine fuel Jet A1 are presented in Table 6 following this description and the examples illustrating the practice of the invention. In said Table 6 are also collected the properties of the jet engine fuels made according to these examples.
Requirements placed on jet engine fuels are becoming more stringent, and means for producing jet engine fuel within a conventional refinery are limited. Hydrocracking units are extremely costly, and the quantities of jet engine fuels made by atmospheric distillation of crude petroleum are limited and depend on the quality of the crudes.
Moreover, refineries whose mode of conversion is based on catalytic cracking have at their disposal only jet engine fuels produced by straight distillation.
In fact, the effluents from a catalytic cracking unit contain very high amounts of aromatics, olefins and sulfur compounds.
Because dearomatization catalysts are based on platinum and are very sensitive to sulfur, sulfur compounds must be removed by previous hydrotreatment.
Such hydrotreatment is exothermic, however, and is therefore difficult to carry out.